Echinacea, also known as purple coneflower, was used by Plain Indians to treat colds and respiratory ailments. In fact, at least 14 native tribes included echinacea among their medicinals. This member of the daisy family (Asteraceae) is native to the central U.S., but flourishes in my northeastern climate as well. (It grows quite prolifically each season in one of my own herbal gardens.) There are nine species to be found in abundance in the U.S. - E. angustifolia, E. pallida and E. purpurea are among the well known. Although these varieties differ in composition and constituents, they offer similar immunostimulating qualities.
The mechanism of action behind echinacea involves its ability to stimulate the production of luekocytes from lymph organs, some of the "good guys" which surround and attack invading bacteria. The herb also promotes chemotaxis , meaning a greater distribution of non-specific immune cells in the blood stream.
There is an abundance of literature that supports the efficacy of echinacea's immunomodulating properties, most notably from 60 years of intensive research and application by German scientists. In vitro studies have shown that echinacea extracts improve phagocytosis , the process by which T-cells secrete enzymes to destroy foreign cells, by 20 to 40 percent. Many studies involving humans demonstrate this herb's effectiveness of preventing illness when taken at the onset of a cold or flu.